1. Field of the Invention
The present invention relates to an impeller of a circumferential current pump used as an in-tank type fuel pump of an automobile.
2. Description of the Prior Art
An in-tank type circumferential current pump having an improved property for being mounted to a vehicle and having a low noise and a small pressure change has been conventionally used in a fuel pump for an electronically controlled type fuel injection apparatus of an automobile.
FIGS. 17 to 19 show a circumferential current pump 51 for an automobile. The circumferential current pump 51 shown in these drawings is placed within a fuel tank (not shown), and is structured such as to apply an energy to a fuel by a vane 54 formed on an outer periphery of an impeller 52 when the impeller 52 is rotated by a motor 53 so as to increase a pressure of the fuel flowing into a pump flow passage 56 from a fuel inlet port 55 and discharge the fuel having the increased pressure to an engine side from a fuel discharge port 57.
In the circumferential current pump 51 mentioned above, in order to maintain a pump efficiency and a discharge pressure in a desired state, it is necessary to set gaps w1 and w2 in a side of side surfaces 58a and 58b of the impeller 52 within a predetermined size so as to reduce a leaked flow amount.
Further, in the circumferential current pump 51 mentioned above, in order to prevent one side surface 58a of the.impeller 52 from being pressed to a pump casing 60 and prevent another side surface 58b of the impeller 52 from being pressed to a pump cover 61 by maintaining the gaps w1 and w2 in the side of the side surfaces 58a and 58b of the impeller 52 in a suitable size, a pressure adjusting hole 62 open to both side surfaces 58a and 58b of the impeller 52 and communicating the gaps w1 and w2 in the side of both side surfaces 58a and 58b of the impeller 52 is formed. In the circumferential current pump 51 structured in this manner, a pressure balance in the side of both side surfaces 58a and 58b of the impeller 52 is achieved by the pressure adjusting hole 62, the impeller 52 smoothly rotates in a state of being a little apart from the pump casing 60 and the pump cover 61, and an abrasion of the side surfaces 58a and 58b of the impeller 52 is prevented, so that a size change caused by the abrasion of the side surfaces 58a and 58b of the impeller 52 is prevented and an improved pump function can be achieved for a long time.
Since the impeller 52 of the conventional circumferential current pump 51 mentioned above is always in contact with the fuel within the fuel tank, a phenol resin or a PPS resin excellent in a solvent resistance is used, whereby the impeller 52 is formed in a desired shape in accordance with an injection molding. Then, the pressure adjusting hole 62 of the impeller 52 mentioned above is formed by a pin 64 stood within a cavity 63 (refer to FIG. 20).
However, as shown in FIG. 20, when the pin 64 for the pressure adjusting hole 62 is at the position apart from an axial hole forming portion 65, a part of a molten resin flow 67 injected into the cavity 63 from an injecting gate 66 is brought into contact with the pin and branched and thereafter the molten resin flow 67 is combined in a downstream side of the pin 64, so that there is generated a disadvantage (a weld phenomenon) that a surface accuracy of the combined portion is deteriorated. Further, in the conventional structure mentioned above, since it is necessary to arrange a plurality of narrow pins 64 within the cavity and a structure of an injection molding metal mold 68 is complicated, the injection molding metal mold 68 becomes expensive, thereby preventing a producing cost of the impeller 52 from being reduced.
Accordingly, an object of the present invention is to provide an impeller for a circumferential current pump which can make a structure of an injection molding metal mold compact without generating a weld phenomenon.
In accordance with a first aspect of the present invention, there is provided an impeller for a circumferential current pump which is provided with a plurality of vane grooves in an outer peripheral side of a synthetic resin disc-like member rotated by a motor and is rotatably received within a substantially disc-like space formed between a pump casing and a pump cover. In this structure, an axial hole engaging with a drive shaft of the motor is formed in a center portion of the disc-like member and a pressure adjusting groove open to both side surfaces of the disc-like member is formed in the axial hole.
In accordance with the present invention having the structure mentioned above, the pressure adjusting groove formed in the axial hole functions so as to keep a balance of a pressure applied to both side surface side of the impeller. As a result, the impeller smoothly rotates in a state of keeping a little gap between the pump casing and the pump cover.
In accordance with a second aspect of the present invention, there is provided an impeller for a circumferential current pump as recited in the first aspect mentioned above, wherein an annular recess portion for arranging a ring gate for an injection molding is formed at a position a predetermined size apart from an outer peripheral side of the axial hole.
Since it is possible to receive a burr within the annular recess portion even when the burr is generated at a time of separating the ring gate for the injection molding, the surface accuracy of the impeller side surface is not deteriorated by the burr.